Gypsum wallboard, comprising a gypsum core and planar paper outer surfaces, is widely and extensively used by the western world building construction industry in the construction of residential and commercial buildings. The gypsum wallboard is typically supplied in half-inch five-eights inch or three-quarter inch thick sheets measuring 4 feet by 8 feet in width and length. The entire wallboard panel can be used in most situations. However, in some situations, only a portion of the wallboard panel can be used, the extraneous portions being cut away by the wallboard installer. Those cut-away parts cannot be used elsewhere. As a consequence, in any building construction or renovation project, a substantial amount of waste gypsum wallboard is generated. As much as 10 percent of the gypsum wallboard panels supplied to the construction site may end up as waste gypsum wallboard.
This waste wallboard has, in the past, created disposal problems in the Greater Vancouver Regional District in British Columbia, Canada, because when the waste wallboard is buried in a conventional waste landfill operation, obnoxious hydrogen sulfide gas and soil leachate are generated. The generated obnoxious gas odour problem has made it necessary to initiate a program of special waste wallboard sorting, stockpiling, storage, and materials handling to facilitate ocean dumping. Currently, in the Greater Vancouver Regional District of British Columbia, approximately 20,000 tons per year of gypsum wallboard waste material is dumped in the Pacific Ocean. This is an expensive waste disposal procedure. It may also lead ultimately to ocean pollution.
The gypsum of the wallboard scraps is valuable and could be reused. However, a serious problem with waste gypsum wallboard is that the paper outer layers remain bonded to the gypsum core and are not readily removable. It is difficult to efficiently remove the paper outer layers from the gypsum core without leaving a substantial amount of paper residue on the gypsum. Gypsum wallboard manufacturers have, to date, been unable to recycle any more than about one percent of the total waste wallboard production because paper contamination of the finished product must be minimized. Such manufacturers currently use a combination of hammer mills and screening plants, which combination, under ideal conditions, is capable of removing about 65 percent of the paper. This process requires considerable energy consumption and creates unwanted airborne gypsum dust.
DE-A-27,09,975, Sep. 14, 1978, discloses a horizontal pair of roughened rollers 28 and 30 which are adjustable in angle to provide a shearing action on a plate 20. No delamination of exterior layers from a core is disclosed.